Ubayu Onsen is a remote hot spring located in a deep mountain valley on the northern side of the Azuma Range in Yonezawa City, Yamagata Prefecture. Situated at an elevation of approximately 1,300 meters, it is one of the highest hot spring resorts in Yamagata Prefecture and is known as a secluded retreat surrounded by rugged mountain scenery.
There is only one accommodation facility at Ubayu Onsen: Masugataya. The inn stands in a dramatic valley surrounded on three sides by steep rock walls. Reddish-brown and gray rock formations rise around the property, creating scenery reminiscent of traditional Japanese landscape paintings.
Behind the inn stretches a primeval forest of Japanese hemlock, beech, and Erman’s birch. Japanese serow can also occasionally be spotted in the surrounding mountains. Waterfalls, unusual rock formations, deep forests, and steep cliffs combine to create an atmosphere reminiscent of a remote mountain sanctuary far from civilization.
One of the greatest attractions of Ubayu Onsen is the spectacular natural scenery that surrounds the hot spring itself. The inn sits in a narrow valley where towering rock peaks rise dramatically on either side, creating a landscape that is both rugged and beautiful.
The scenery is particularly impressive in spring, when fresh green leaves appear, and autumn, when the mountains turn brilliant shades of red and yellow. In summer, the high elevation provides a cool mountain environment where visitors can enjoy the clean air and abundant nature.
There are six spring outlets emerging from the surrounding rock walls, producing a plentiful supply of hot spring water. One of these sources is used by Masugataya, while the remaining water flows down into the nearby river.
The total volume of spring water is approximately 300 liters per minute, with a source temperature of around 51°C. The slightly bluish, milky-white water has a natural appearance that perfectly complements the wild mountain setting.
At Ubayu Onsen, guests can enjoy free-flowing hot spring water directly from the source, without adding water or heating the spring water. The spring is classified as a simple hot spring (low-osmotic, acidic high-temperature spring).
The bathing facilities include three outdoor baths and indoor baths, all supplied with free-flowing hot spring water. As you soak in the naturally heated water, you can listen to the sound of the river and birdsong while looking out over the dramatic mountain valley.
This combination of natural surroundings and open-air bathing offers a sense of freedom that is quite different from the experience of a conventional urban spa.
One of the most memorable baths is Yamamba-no-Yu, a mixed-gender outdoor bath. It is located in a dramatic setting surrounded on three sides by steep cliffs and unusual rock formations.
Bathing while looking directly at the rugged rock peaks is a unique experience. The immense landscape, seemingly shaped entirely by nature, is one of the defining attractions of Ubayu Onsen.
Ubayu Onsen takes on a different character with every season. In spring, young leaves emerge and the mountains are covered in vibrant fresh greenery. Summer brings cool mountain air and an opportunity to enjoy the surrounding forests and wilderness.
In autumn, the surrounding trees turn shades of red and yellow, creating a spectacular autumn foliage landscape against the rugged rock peaks. At night, the remote location and lack of artificial light also make it possible to enjoy a spectacular star-filled sky.
Surrounded by deep valleys, primeval forests, and dramatic rock formations, Ubayu Onsen is a place where visitors can experience the changing seasons while relaxing in a natural mountain hot spring.
Masugataya has a long history. The opening of Ubayu Onsen is traditionally dated to 1533, during Japan’s Sengoku period. Despite its remote location at an elevation of approximately 1,300 meters, the hot spring has been carefully maintained for centuries.
Ubayu Onsen has an intriguing legend associated with the origin of its name. According to tradition, the founder of Masugataya was searching for gold in the mountains when a mysterious yamamba, or mountain hag, revealed the existence of the hot spring to him.
This story is said to be connected with the name “Ubayu,” giving the remote hot spring an even more mysterious atmosphere. The legend continues to be passed down alongside the long history of the mountain retreat.
Masugataya is the only inn at Ubayu Onsen, offering visitors the opportunity to stay in a quiet mountain environment surrounded by nature. The inn has 13 Japanese-style rooms, each equipped with a toilet.
Unlike a conventional hot spring town with numerous hotels, restaurants, and shops, Ubayu Onsen offers a remarkably peaceful atmosphere. The scenery and silence that can only be experienced after traveling deep into the mountains are an essential part of the attraction.
Because Ubayu Onsen is located high in the mountains, the area receives heavy snowfall during winter. Masugataya is generally closed from around early November until late April, making the hot spring inaccessible during the snow-covered season.
For this reason, the best time to visit is generally from spring through summer, when the mountains are covered in fresh greenery, or in autumn, when the foliage becomes vibrant. Before traveling, visitors should check the inn’s operating period and current road conditions.
Ubayu Onsen is one of Yamagata’s best-known secluded hot springs, hidden deep within the mountains of the Azuma Range. The dramatic landscape of towering rock formations, primeval forests, waterfalls, and steep valleys at an elevation of approximately 1,300 meters creates an atmosphere that is difficult to experience at ordinary hot spring resorts.
In the open-air baths supplied directly by the abundant natural hot spring source, visitors can relax while listening to the flowing river and birdsong and looking out over the spectacular mountain valley.
With its historic solitary inn, the legend of the yamamba, and the changing beauty of fresh greenery, autumn foliage, and star-filled skies, Ubayu Onsen offers a rare opportunity to slow down and experience the peaceful atmosphere of a remote Japanese mountain hot spring.